The present invention relates to a system for measuring tritium radioactivity.
Tritium radiates soft .beta. rays having an average energy of 5.7 KeV. The radioactivity of tritium is generally measured by a batch system using a detector which is filled with a gaseous tritium sample or a liquid scintillator dissolving the sample gas.
The detector used with the batch system for the gaseous tritium sample is a Geiger Muller tube, a proportional counter or an ionization chamber, and the detector for the liquid sample is a liquid scintillation counter.
Although the counting efficiency of the liquid scintillation counter is generally low, it has been widely used because the chemical form of the sample can be relatively freely selected. However, in addition to the low counting efficiency thereof, the liquid scintillation counter is generally very expensive. Furthermore, in the measurement of tritium, there are problems in precise correction for the quenching effect, and with the inflammable radioactive organic liquid left after the measurement. Therefore, it is economically difficult to continuously measure a number of samples by the liquid scintillation counting method and, even if this difficulty is overcome, there are problems of radioactive contamination and safety.
Compared with the liquid scintillation counting method, the measuring method using the ionization chamber, which is theoretically simple in construction and inexpensive in manufacture, is inherently safe. However, it is known that the sensitivity of the ionization chamber is low, and the constituents of the sample whose radioactivity is to be measured are limited.
The method using the proportional counter exhibits considerably higher sensitivity and lower background noise than those of the other systems including the ionization chamber system, and there is no problem in safety management. However, the chemical form of the measurable sample is limited compared with that which can be measured by the ionization chamber system. Therefore, if the limitations in the chemical form of the sample were removed, it would be possible to use the proportional counter system very effectively.
The chemical form of the sample to be measured by the proportional counter system is hydrogen gas or gaseous lower hydrocarbons such as acetylene, ethane, methane or propane, etc., and depends upon the counting characteristics of the counter. These forms are generally provided by using decomposition reactions such as oxidation or reduction, etc., or organic synthesizing reactions together with a decomposition reaction, which requires a troublesome operation under very severe conditions making it practically disadvantageous. Further, it is difficult to prepare these chemical forms continuously through these operations, causing the application thereof to the continuous measuring system to be limited.